David Keith McCallum, Jr. (born 19 September 1933) is a Scottish actor and musician. He first gained recognition in the 1960s for playing Russian spy Illya Kuryakin, a Russian secret agent, in the television series The Man from U.N.C.L.E. and as interdimensional operative Steel in Sapphire & Steel.

In recent years, McCallum has gained international recognition and popularity for his role as NCIS medical examiner Dr. Donald "Ducky" Mallard in the American television series NCIS.